The terms “sub-surface formation” and “downhole formation” typically refer to the rock formation around a bore which has been drilled into the ground. The borehole provides a path for hydrocarbons, such as oil and gas, in the rock formation to be brought to the surface. Sub-surface formations from which hydrocarbons are produced, typically contain a fluid which includes liquid and gas mixed together. The liquid from the downhole formation will normally require pumping to bring it from the downhole formation to the surface. Pumps used for pumping the fluid from the downhole formation to the surface, such as progressing cavity pumps, piston pumps or electric submersible pumps, operate more efficiently if there is no gas in the fluid being pumped. Also, the presence of gas in the fluid being pumped can damage the pump, through heat generation, cavitation or gas absorption.
There are various devices known for separating gas from liquid in a downhole application. See, for example, U.S. Pat. No. 5,902,378 to Obrejanu, incorporated herein by reference in its entirety.
Typically, the more gas which can be eliminated from the fluid, the better the operation of the pump.